Axle driving units incorporating hydraulic stepless transmissions have been used to drive the axles of self-propelled vehicles for many years. Generally such units include a hydraulic pump driven by an input shaft and a hydraulic motor having an output shaft drivingly connected through a differential to a pair of oppositely disposed axles. An example of such a unit is disclosed in U.S. Pat. No. 4,914,907. However, certain self-propelled vehicles perform tasks which require tight turning capabilities and conventional hydraulic transmissions which drive a pair of axles through a differential gear assembly are not particularly suited for such purposes. Instead, vehicles have been provided with axles which are independently driven by separate axle drive units such that turns are accomplished by rotating drive wheels on opposite sides of the vehicle at different speeds and/or in different directions. Further, certain such axle driving units for independently driving single axle have incorporated hydraulic transmissions. However, such axle driving units have required housings which are of substantial height and substantial width in order to accommodate the hydraulic pump and motor and the other necessary components. Accordingly, vehicles have required large body frames in order to accommodate two such axle driving units in a side-by-side disposition, thus ruling out use of the units on many small vehicles. Further, even where a large body frame is provided, the center of gravity of the vehicle tends to be higher than is desirable for good roadability due to the height of the axle driving units and the need to dispose the prime mover of the vehicle in an elevated position to efficiently drive the units. For example, in U.S. Pat. No. 5,127,215 a dual hydrostatic drive walk-behind mower is disclosed, but it can be readily seen that the axle driving units of this mower require substantial vertical and lateral space such that a large body frame is required. It will also be noted that due to the height of the transmission housings, the engine must be disposed in an elevated position which results in the vehicle having an undesirably high center of gravity. Moreover, multiple driving belts are required to drive the input shafts of the axle driving units. (See also, U.S. Pat. Nos. 4,809,796 and 5,078,222). In U.S. Pat. No. 4,819,508, a transmission system for working vehicles is disclosed which partially solves the problem of an undesirable center of gravity by reorienting the engine such that the crank shaft is horizontally disposed. However, the axle driving mechanism still occupies substantial vertical space on the body frame, making the center of gravity undesirably high. Further, reorientation of the engine complicates the drive belt systems for driving both the axle driving units and the mower blades.
Therefore, it is an object of the present invention to provide an axle driving apparatus for independently driving axles on opposite sides of a vehicle.
It is another object of the present invention to provide an axle driving apparatus which includes side-by-side axle drive units incorporating hydraulic transmissions which require limited vertical or lateral space such that the axle driving apparatus can be used by small self-propelled vehicles, and such that vehicles utilizing such axle driving apparatus define low centers of gravity for improved roadability
Yet another object of the present invention is to provide an axle driving apparatus having input shafts and a drive belt system which facilitates drivingly connecting the apparatus to the prime mover of the vehicle.
Still another object of the present invention is to provide an axle driving apparatus which is inexpensive to manufacture and maintain.